1. Field of the Invention
The present invention relates generally to the audio synthesis of signals. More particularly, the present invention relates to the audio synthesis of signals, which correspond to navigation and/or communication frequencies.
2. Background of the Invention
Transportation vehicles, such as airplanes, water crafts, and ground vehicles, often depend upon signals (or beacons) to facilitate accurate navigation. For example, an airplane may receive satellite, ground, or airborne navigation signals from various navigational aids, which enables the airplane to determine bearing, heading, distance vectors, location, and so forth. Similarly, these vehicles may also employ a communications system, which facilitates communication to and from the vehicles.
Navigation and communication systems typically operate at set frequencies or over a range of frequencies. These systems can be manually or automatically tuned to a particular frequency. For example, as shown in FIG. 1, system 1 (e.g., a navigational system, a communications system or a navigation/communications system) includes a receiver (and/or a transceiver) 2, a display device 3, and a frequency selector 4 (e.g., a knob, dial, key pad, digital selector, analog selector, and so forth). A frequency selector 4 in the form of a dial may include a plurality of detent clicks 4a, each of which corresponds to a frequency step. The display device 3 is of a known variety, such as a LED, liquid crystal, active matrix, thin film, and so forth. Such a display device 3 may be integral to system 1, as shown in FIG. 1, or may be an external device, which is not part of system 1. Of course, system 1 may include multiple display devices and corresponding multiple frequency selectors. System 1 may also include other components, such as a microprocessor, frequency tunning circuitry, and so forth.
An operator (e.g., a pilot) manipulates or turns the selector 4 to tune the system 1 to a particular frequency. Typically, the currently tuned or selected frequency is displayed via the display device 3. For purposes of this discussion, a “currently tuned frequency” includes a frequency at which the radio is presently tuned to, and/or a frequency which is selected by an operator. If the system 1 is tuned to 900 MHz, “900 MHz,” “900,” “9,” or some other “indicator” will be displayed via the display device 3. In this manner, an operator obtains visual feedback of a selected frequency.
A display device 3 failure may occur during the operation of system 1. Such a failure hampers the selection of a navigation/communication frequency, since an operator is unable to visually determine (or confirm) the currently tuned frequency. A conventional mechanism for handling such a display device 3 failure requires the operator to initiate an “emergency mode.” In the emergency mode, the system 1 is reset to a predetermined frequency. The operator then manually counts up or down from the predetermined frequency to tune the radio. For example, the operator turns the frequency selector 4, and counts the number of detent clicks 4a to determine the currently tuned frequency. This conventional process fails to provide the operator with an adequate feedback mechanism for determining the currently tuned frequency. As a result, frequency selection is hampered. Moreover, without a feedback mechanism to alert the operator of the currently tuned frequency, the safety of the operator and passengers may be jeopardized.
Accordingly, there is a need for a feedback mechanism for a currently tuned frequency when a display device fails. There is also a need for an audio indication of the currently tuned frequency. There is a further need for a procedure for controlling feedback in a navigation and/or communication system during a display device failure.